Add wekan-ical-server

[dumprop]

https://github.com/wekan/wekan-ical-server
https://github.com/wekan/wekan/wiki/Time-Tracking
I think it will be useful to have calendar integration out of the box

[yalh76]

Feel free to do a PR to add calendar integration

[Limezy]

I would like to take a look at this.
@yalh76 do you think it would be better to have it as a separate yunohost app ?
Or should it be shipped out of the box with wekan_ynh ?

[yalh76]

no idea if it's better to have it in wekan_ynh or in a dedicated package